Environmental Remediation Potential of Engineered Nanoparticles: Benefits, Challenges, and Risks.

Novel reactive nanomaterials, such as Fe⁰ nanoparticles (NZVI), offer the potential for highly efficient targeted delivery of remedial agents to subsurface contaminants.  The primary challenge to application is selecting appropriate nanoparticle surface modifiers that enable emplacement in the contamination zone and afford some affinity for the contaminant of interest, but do not adversely impact the particle’s reactivity with the contaminant.  Choosing appropriate surface coatings can also decrease the potential toxicity of the particles. Concomitant optimization of mobility, reaction selectivity, while minimizing toxicity requires a fundamental molecular level understanding of the surface modifiers properties and how they affect nanoparticle deposition. Dynamic light scattering and electrophoretic mobility measurements, along with Ohshimas’s analysis are used to characterize the layer conformation and properties of different types of common synthetic and natural polyelectrolytes adsorbed onto NZVI.  Batch reactivity studies and column and 2-D flow cell studies under a variety of hydrogeochemical conditions and heterogeneities were then conducted on polyelectrolyte-modified NZVI to determine the effect of the adsorbed layer properties and injection conditions on reactivity and mobility.  Surface coatings decreased particle reactivity with TCE by up to a factor of 20, and eliminated the particles bactericidal properties.  However, surface coatings also decrease the adverse effects of water solutes (e.g. natural organic matter) on particle reactivity.  The magnitude of the effect depended on the adsorbed layer conformation of the polyelectrolyte as explained using the Scheutjens and Fleer train-loop-tail conceptual model for homopolymer sorption.  This study emphasizes the important role of organic macromolecular surface coatings on aggregation, nanoparticle transport, and the potential toxicity of NZVI used for groundwater remediation.